The power output of RADAR, communications transmitters, or transceivers may be monitored to provide built-in test capabilities and to ensure that the power transmission meets a specified system requirement. Such monitoring capabilities may also be used for calibration.
Known transmitters or transceivers that share a port for transmission and reception use a switch to direct the radio frequency (RF) signal from transmit power amplifiers to the port and from the port to receive amplifiers. These systems may involve RF couplers between the transmit/receive switch and the output port to direct a small portion of the RF signal to a detector diode that is connected to an amplifier. For example, U.S. Patent Pub. No. 2004/0077316 to Xiong shows a separate, coupled power detector diode to monitor power levels. Any coupler or device between the transmit/receive switch and the output port reduces the transmit signal by coupling loss as well as insertion loss of the coupler. When the path is used for both transmit and receive signals, the coupler can reduce input power and increase receiver noise, causing degradation in both paths.